There is known a method of determining the deformation characteristics by single-axis loading of a specimen and measuring its deformation, with a thoroughly prepared specimen having the load applied to its face surfaces. The test includes measuring the deformation of the specimen and registering the corresponding load. The outcome of the test is used to determine such deformation characteristics as the modulus of elasticity and the deformation modulus.
The known method would not enable determining the deformation characteristics of a material in a structure. Moreover, the method in certain cases involves errors, such as those associated with the testing of concrete, on account of the lack of sufficient consistence of the properties of concrete in specimens and in real-life structures, caused by unavoidable differences among the conditions of placing, compacting and setting of the concrete in specimens and structures.
A method not unlike the abovementioned one is the laboratory method of studying the deformation properties of soils, called the compression method. A soil specimen taken from a test pit or hole is placed into a compression device and subjected to a load. The varying load and the accompanying variation of the height of the specimen are used to evaluate the deformation properties of the soil being tested.
However, the handling and storage of a specimen, as well as the operation of placing the specimen into the testing device more often than not alter the properties of the soil, which affects the practical value of this known method. Moreover, not every kind of soil can be sampled as a specimen retaining the natural properties of the soil, and with some soils such specimens cannot be taken altogether.
Therefore, the practice of engineering and geological studies makes use of the so-called pressiometric, or pressure-metering method of field-testing of soils in situ. The method is based on introducing into a predrilled hole a bladder or cylinder readily deformable in the horizontal direction. The variation of the volume of this bladder or cylinder at specified values of the pressure supplied thereinto is used to determine the deformation properties of the soil in the horizontal direction. The method is valid in what concerns isotropic soils which are also expected to be secure enough to sustain the uncased walls of the borehole. In real life, however, we have to deal more often than not with anisotropic soils displaying different properties in the horizontal and vertical directions. The abovementioned pressiometric method might lead to considerable errors when used for investigating the properties of anisotropic soils.
The closest prior art of the present invention is the technique of testing the soil in situ, in a test pit or a borehole, with the use of dies (cf. "Field Methods of Investigating Construction Properties of Soils" by Y. G. Trofimenkov and L. N. Vorobkov, in Russian, STROYIZDAT Publishers, Moscow, 1974, p. 57).
The method includes preparing the testing area by providing either a test pit or a drilled hole, stripping the contact surface, placing a die, loading the die with an increasing load, measuring the displacement of the die and computing the deformation modulus for the rectilinear portion of the curve showing the relationship between the displacement of the die and the load.
The diameter of the testing die used in the present-day practice of engineering and geological studies by this technique may be from 300 mm (in a hole) to 800 mm (in a test pit).
However, the outcome of the test is significantly influenced by the initial conditions of the testing cycle, such as the initial loose contact between the soil and the bottom of the die, and also the affected structure and loosening of the soil within a certain volume, caused by the drilling of the hole.
Besides, the method is labor-consuming and takes considerable time for a single testing cycle, whereby it is predominantly used in the engineering practice only in cases where engineering and geological studies are conducted in association with some unique construction project.
Nevertheless, the problem of obtaining sufficient information on the deformation properties of a material or soil remains quite acute. When this information is available, it is possible, for instance, to reduce the cost of a structure or a building without affecting the degree of its practical reliability in service.
The assessment of the joint and interrelated work of ground-supported structures, the foundation and the soil base enables to arive at the best possible engineering solution. With sufficient information available, the adverse effect of non-uniform sagging of the soil foundation may be positively minimized, which enables to require less of the shielding and guarding structures; the heat- and sound-insulating properties of the structure may be enhanced, and the level of the strained state in statically indeterminable load-supporting structures may be reduced.
Furthermore, dependable information on the deformation properties of the soil at the base of a structure enables in most cases to have higher service loads applied to this base of the structure.